<script language="JavaScript">
function mouseDown(evt) {
	var evt = evt||event;
	shiftPressed=evt.shiftKey;
	altPressed  =evt.altKey;
	ctrlPressed =evt.ctrlKey;
	if (shiftPressed || altPressed || ctrlPressed) 
		alert ("Mouse clicked with the following keys:\n"
			+ (shiftPressed ? "Shift ":"")
			+ (altPressed   ? "Alt "  :"")
			+ (ctrlPressed  ? "Ctrl " :"")
		)
	return true;
}
 document.onmousedown = mouseDown;
</script>